The interesting association of absence of HLA tissue type-A1 with chronic Chagas' disease was not confirmed by an expanded study of cases, but DR (B cell) typing will still be done on frozen cells. The diversity of HLA haplotypes encountered in this Brazilian patient population corroborates what anthropologists have said of this population - namely, extreme genetic mixing. Further study of different antigenic fractions of schistosome worms has disclosed one fraction to which antibody levels in patients correlate quite well with numbers of eggs being excreted, or intensity of infection. Evidence for serum inhibitory factors and for suppressor cells has been found in filariasis patients characterized by unresponsiveness to filarial antigens. The role of immune complexes in filariasis patients is also being studied. Serum and cell factors were also found that contributed to antigen unresponsiveness in patients with chronic schistosomiasis.